Method and apparatus for coding in a telecommunications system

ABSTRACT

First and second transmission links are established with a remote station. An information signal is encoded to provide an encoded information signal having more bits than the information signal. First and second transmission signals are provided wherein each transmission signal has bits selected from the encoded information signal. Each of the first and second transmission signals is transmitted to the remote station by way of a respective one of the first and second transmission links. The remote station receives and combines the first and second transmission signals transmitted by the remote station to provide a combined encoded signal. The combined encoded signal is decoded by the remote station to provide the information signal. The first and second transmission links can be formed between the remote station and a single base station or between the remote station and two separate base stations.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation of priorapplication Ser. No. 10/848,951, entitled “Method and Apparatus forCoding in a Telecommunications System”, filed May 18, 2004, now U.S.Pat. No. 7,161,993 issued Jan. 9, 2007, which is a Divisional of U.S.application Ser. No. 10/386,998 entitled “Method and Apparatus forCoding in a Telecommunications System,” filed Mar. 11, 2003, now U.S.Pat. No. 6,757,335 issued Jun. 29, 2004, which is a Continuation of U.S.application Ser. No. 09/547,824, entitled “Method for Coding in aTelecommunications System,” filed Apr. 7, 2000, now U.S. Pat. No.6,560,292 issued May 6, 2003, all assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates to communications in general and, inparticular, to improving the transmission of information signals in acommunications system.

2. Background

The quality of a communication link over a noisy channel depends on theenergy to interference noise ratio Eb/No of the signal. To achieve arequired bit error rate over the communication link, a particular Eb/Nois required. The bit error rate is a function of several parametersincluding channel propagation characteristics. In order to reach thetarget Eb/No a transmitter must transmit a signal with sufficient power.In practice, communication systems of this type are power limited. Inpower limited systems the transmitter cannot necessarily transmit theamount of power required to maintain a desired bit error rate. In CDMAsystems, the sum of the power required by each link in the systemdetermines the overall capacity of the system. Thus, it is desirable foreach communication link to require the lowest Eb/No possible.

In order to decrease the required Eb/No in CDMA systems, the data to betransmitted can be encoded. Many different encoders are known in theart. For example, conventional convolutional and turbo encoders aresuitable for this purpose. All of the suitable encoders perform the samebasic task of creating redundancy in the encoded information signal. Insuch encoding techniques, each encoded bit is a function of a pluralityof input bits.

For example, the encoder system 1 of FIG. 1 can be used to provide aredundant encoded signal suitable for use in decreasing the requiredEb/No in a CDMA communication system. The rate R encoder 4 of theencoder system 1 receives a stream of k information bits 2 and outputs alarger stream 6 of n coded bits wherein R is the code rate. The coderate R is the ratio of the number of information bits k per unit of timeto the number of coded bits n per unit of time. Thus R=k/n, and n=k/R.The n bits of coded bit stream 6 at the output of the rate R encoder 4can be transmitted over the transmission channel 8. A rate R decoder 12performs a decoding operation that is the inverse of the operationperformed by the rate R encoder 4. That is, the rate R decoder 12converts the received n coded bits 10 into k information bits 14 thatare substantially equivalent to the k information bits 2 that were inputto the rate R encoder 4. In CDMA systems, typically the rate R=½ or R=⅓.

It is known that for similar encoding techniques a lower code rate Rpermits a lower Eb/No to obtain the same bit error rate (where it isunderstood that ⅓ is a “lower” rate than ½). However, this improvementin performance becomes negligible when the code rate R becomes too low.Typically little further improvement occurs below R=⅙. Furthermore,since the number of encoded bits increases as the code rate R getssmaller it is usually not desirable or even possible to transmit thelarge number of coded bits required for code rates lower than R=⅙.Typically, code rates of ½ and ⅓ are preferred.

Although the use of a lower code rate is desirable, because it wouldlower the required Eb/No in a CDMA communication system, it is deemedundesirable to use a lower code rate if doing so would have an overalladverse effect, such as lowering system capacity.

Lower code rates generate more bits for transmission than do higher coderates.

For example, if the code rate on a system were decreased from ½ to ¼, itwould double the number of coded bits needed to be transmitted by thesystem. Thus, bandwidth between the remote station and the base stationwould need to be doubled in order to support such a decrease in coderates.

In a CDMA system, one could double the effective bandwidth on theforward link by halving the length of the Walsh codes used fororthogonally spreading the encoded bit stream. For example, by halvingthe length of the Walsh codes used in a CDMA system from 64 bits to 32bits, a given data stream could be transmitted over the forward link inhalf the number of coded bits. Although decreasing the Walsh code lengtheffectively increases the bandwidth between the remote station and thebase station, it is undesirable to decrease the Walsh code lengthbecause doing so decreases the pool of Walsh codes. As is well known inthe art, a decreased pool of Walsh codes decreases the number of usersthat the system can support. When a system has allocated all of itsWalsh codes to users, no more users can be added to the system becausethe system is said to be “code limited”.

Since the number of spreading codes in a system is limited, theadvantages of any gain achieved with a low code rate R can be offset bythe disadvantage of the use of additional spreading codes. Thus,although decreasing the code rate R used by each user in a CDMAcommunication system improves the required Eb/No per user, it can alsolimit the number of users by creating a shortage of spreading codes.Although there exists ways of creating more spreading codes, such as byusing quasi-orthogonal functions or by using multiple scrambling (PN)codes, these techniques are used as a last resort because theysignificantly increase the overall interference level in the system.

Besides being code limited, a system may be limited in the number ofusers it can support at a given time due to limits in the amount ofpower that the base station can transmit. Transmitting more power thanis allowed will cause interference that cannot be tolerated by theadjacent cells. When a new user is added to the system, the amount ofpower that is transmitted by the base station will increase. Becausethere is a limit on the amount of power that the base station cantransmit, the number of users may be limited by the total amount ofpower that can be transmitted. Therefore, even if there are additionalspreading codes available, the number of users will be limited by theamount of power that can be transmitted by the base station. When a basestation is limited in the number of users it can support at a given timedue to power transmission limitations, the system is said to be “powerlimited.”

To improve the performance of a telecommunication system—performancewhich is usually measured in Erlangs, bits per seconds, or number ofusers—it is necessary to take into account both code limitations andpower limitations. What is desired is a way to increase the systemperformance of a telecommunications system, often measured in the numberof users that a telecommunications system can simultaneously support, bytaking into account the fact that the system is both code limited andpower limited.

SUMMARY

A method is taught for improving the transmission of information signalsin a communications system having a base station and a remote station.First and second transmission links are established with the remotestation. A base station information signal is encoded to provide anencoded information signal having more bits than the information signal.First and second transmission signals are provided wherein eachtransmission signal has bits selected from the encoded informationsignal. The first and second transmission signals are each transmittedto the remote station by one of the first and second transmission links,respectively. The remote station receives and combines the first andsecond transmission signals transmitted by the remote station to providea combined encoded signal. The combined encoded signal is decoded by theremote station to provide the information signal. The first and secondtransmission links can be formed between the remote station and a singlebase station or between the remote station and two separate basestations.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent form the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify corresponding elements throughout and wherein:

FIG. 1 shows a conventional information bit stream encoder systemsuitable for encoding signals in a wireless communications system;

FIG. 2 shows a block diagram representation of a method for transmittinginformation in a wireless communications system;

FIG. 3 shows a code generator system using puncturing of a lower codesignal to provide a required signal;

FIG. 3A shows a flowchart of a method for forming a lower rate R codedbitstream by a code generator system.

FIG. 4 shows a wireless communications system wherein the method of thepresent invention can be advantageously applied; and

FIG. 4A shows a method for decoding a lower rate coded bitstream.

FIG. 5 shows an alternative block diagram representation of a method fortransmitting information in a wireless communications system.

FIG. 6 is a block diagram showing a simplified illustration of a remotestation.

FIG. 7 is a block diagram of a portion of a digital demodulator and aWalsh despreading unit that can be used to receive data in the receiveddata detection mode of the present embodiments.

FIG. 8 is an exemplary embodiment of a dot product.

FIG. 9 is a block diagram of a portion of a digital demodulator and aWalsh despreading unit that can be used to receive data in the receiveddata detection mode of the present embodiments.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a block diagram of a signal transmission method 240 inaccordance with one embodiment of the present invention. In signaltransmission method 240, a base station information bit stream to betransmitted to a remote station is received for encoding in block 242.The process then moves to block 244.

In block 244 the information bit stream is encoded into a lower rateencoded bit stream to decrease the required Eb/No needed to transmit thebits to a remote station (as mentioned earlier, a lower code rategenerates more bits than a higher coderate but requires less transmitpower to achieve the same quality of service). In an exemplaryembodiment, the encoder is a rate ¼ turbo encoder. In alternateembodiments, various encoder rates and types can be used. In anexemplary embodiment, the encoder has a property such that the odd bitsof the ¼ rate encoded bit stream make up a ½ rate encoded bit stream,and the even bits make up a second ½ rate encoded bit stream. In otherwords, bits 1, 3, 5, etc. make up one ½ rate encoded bit stream and bits2, 4, 6, etc make up a separate ½ rate encoded bit stream. All of thebits, however, comprise the ¼ rate encoded bit stream. In theaforementioned embodiment, the ¼ rate encoded bit stream is the lowerrate encoded bit stream referenced earlier. In alternate embodiments thebits are arranged such that a different combination of the bits makes upthe two ½ rate streams (e.g., the first n/2 bits comprise one ½ rateencoded bit stream, while the second n/2 bits comprise a second ½ rateencoded bit stream). In the above exemplary embodiments, the fact thatthe lower rate encoded bit stream comprises at least one standard bitencoded bit stream allows the encoder to produce only a single bitstream that could be used for transmission on two channels as laterdescribed in reference to block 250 and which also could have a portionof it used for transmission on a single channel in block 252. In yetanother alternate embodiment, the encoder produces two separate bitstreams, one encoded at a lower rate and one encoded at a standard rate(e.g., ¼ rate and ½ rate, respectively). In this alternate embodiment,the lower rate encoded bit stream need not comprise two standard rateencoded bit streams. In this embodiment, the lower rate encoded bitstream would be used for transmission when the process branches to block250 and the separate standard rate encoded bit stream would be used fortransmission when the process branches to block 252.

The process then moves from block 244 to decision block 246. Block 246is representative of a decision block wherein it is determined whether asingle standard rate encoded bit stream should be transmitted on asingle channel or whether a lower rate encoded bit stream should betransmitted in portions over two channels. Any parameter(s) within aCDMA communication system can be used as the basis of the decision indecision block 246. The only criterion for selecting a parameter for usein decision block 246 is whether the parameter can be used to optimizethe communication system in some way. Thus, the quality determinationmade in decision block 246 can be made based on any one of a largenumber of different quality factors. A straightforward way to make thedecision is to have the transmitter recognize that it is transmitting ata high power level (for example, recognizing that more than 10% of thebase station's transmit power capacity is being used on any given remotestation), and that it should switch from one transmit stream to twotransmit streams.

In one embodiment, in block 246, it is determined whether the amount oftransmit power that would be utilized to transmit the data as a singlestandard rate encoded bit stream is above a predetermined threshold. Thepower level of the transmission is increased as necessary in order tomaintain a desired bit error rate, but the power level can not beincreased without limit. Thus, in decision block 246 a determination ismade as to whether “excessive” transmission power is required tomaintain the bit error rate. If the transmission power is deemed“excessive,” then the process proceeds to block 250, wherein the lowerrate encoded bit stream is transmitted on two channels.

In one embodiment, in decision block 246 it is also checked whether thenumber of spreading codes presently available is above a pre-determinedfirst threshold value. In such a case, not only must “excessive” powerbe determined, but also the number of available spreading codes must beabove the first threshold value in order for the process to move toblock 250. The first threshold value is zero in one embodiment, meaningthat there must be at least one available spreading code. This check isdone because, although it is desirable to reduce power by transmittingdata over two channels, a code needs to be available to allocate to thesecondary channel.

In one embodiment, it is determined in decision block 246 whether theremote station is in soft-handoff or in softer-handoff. As is known inthe art, when a remote station is in soft-handoff or softer-handoff, aremote station has communication channels open with more than one cellsite sector. Hereinafter, soft-handoff shall be used to refer to bothsoft-handoff and softer-handoff. If it is determined that a remotestation is in soft-handoff, then the process moves to block 250. Thereason the process moves to block 250 is as follows. In a conventionalsystem, each sector would transmit the same standard encoded bit streamusing one channel (Walsh code) per sector. Using the method of thepresent embodiment uses no extra channels in this instance, because onlytwo channels are needed, and they would have been used in theconventional system during soft-handoff anyway. Proceeding to block 250thus does not use any extra channels, yet it yields the gain describedin reference to block 250 below. Namely, less power can be used whentransmitting a lower encoded rate bit stream than when transmitting astandard encoded rate bit stream. This relationship holds true even whenthe same standard encoded bit stream is transmitted on multiplechannels, as it is in a conventional system while a remote station is insoft-handoff. Thus, due to the increased system performance from thepower savings that can be obtained, the process moves to block 250 whenthe remote station is in soft-handoff.

In one embodiment a pre-determined second threshold value can be used inblock 246 to determine whether or not to move to block 250 irrespectiveof whether or not it is determined that “excessive” power is being usedto transmit to the remote station. In such a case, if the number ofavailable spreading codes is above the second threshold value, thusindicating that using an extra code for the call in question wouldlikely not cause a shortage of codes that would reduce system capacity,then the process would proceed to block 250, irrespective of whether theamount of power being used to transmit to the remote station isexcessive. In this case, although the transmitter's power might not beexcessive, reducing the transmitter's power by any amount will stillbenefit the wireless system because it reduces the likelihood ofinterfering with other cells. Because there is presently no shortage ofspreading codes, and the likelihood is low that there will be a shortageof spreading codes anytime soon (as determined by comparing the numberof available codes with a second threshold value), it is beneficial touse one of the spreading codes to reduce transmit power, thus increasingsystem performance.

One skilled in the art will appreciate that decision block 246 can useany combination of the above embodiments, or it can use any otherembodiments that can determine whether transmitting data to a particularremote station across two channels will optimize the communicationsystem, to decide whether or not to proceed to block 250 in which thelower rate encoded bit stream is transmitted on two channels. One simpleembodiment that can be used in decision block 246 is to check thesetting of a flag, variable, or register, to determine whether or notthe communication system will benefit from transmitting data to aparticular remote station across two channels. This is useful in acommunication system wherein a complex determination is first made thattwo channels should be used for transmission, after which a singleindicator bit, or a message containing multiple bits, both of which arehereinafter referred to as an indicator message, is sent to the remotestation to indicate that a lower rate encoded bit stream will betransmitted on two channels at a predetermined point in time in thefuture. A flag is then set in the telecommunication system to indicatethat future bit streams should be transmitted across two channels at apredetermined point in time. In such a case, just a flag would need tobe checked in block 246.

If, in block 246, it is determined that the communication system willbenefit from transmitting data to a particular remote station across twochannels, the process proceeds to block 250. Otherwise, the processproceeds to block 252.

In block 250, the telecommunications system uses a mode of communicationwith the base station such that a first portion of the lower rateencoded bit stream is transmitted on a primary channel, while a secondportion is transmitted on a secondary channel. In one embodiment, thetwo separate standard rate encoded bit streams that make up the lowerrate encoded bit stream are transmitted over a primary and secondarychannel. For example, if the lower rate encoded bit stream is a ¼ ratebit stream comprising both a standard ½ rate encoded bit stream in itsodd bits and a standard ½ rate encoded bit stream in its even bits, thenthe odd bits of the stream would be transmitted over a primary channeland the even bits would be transmitted over a secondary channel. In theaforementioned embodiment the portions transmitted are of equal length.However, the present invention is not limited to such an embodiment. Inalternate embodiments, portions of varying length can be transmitted onmultiple channels. For instance, an encoded bit stream could have onethird of its bits transmitted on a primary channel and the remaining twothirds of its bits transmitted on a secondary channel.

The use of two channels rather than one results in a higher gain withinthe communication system. The second transmission channel can beestablished when needed or it can already be in use.

After the encoded bit streams are formed for each channel, each bitstream is transmitted in accordance with traffic channel requirementsfor the specific system at hand. For example, as is known to one skilledin the art, in a cdma2000 system the forward link channel's encoded bitstream is interleaved, covered with a Walsh code, spread with a PNsequence, and digitally modulated using Quadrature Phase Shift Keying(QPSK). It will be understood that performing signal transmission inthis manner requires a base station to use two Walsh codes rather thanone, because two channels are being used instead of one. Furthermore, itwill be understood that when performing signal transmission is thismanner, the transmit power of each of the transmission channels of block250 can be less than one half the transmit power needed to maintain adesired bit error rate had only a single channel been used. Thus, thepeak power requirement for transmitting the encoded information signalis reduced by more than one half

When transmitting data in this mode, the communication system needs toindicate to the remote station that it needs to begin receiving bitstreams at a lower code rate, wherein the bit stream are transmitted inportions amongst multiple channels. As stated in relation to block 246,this indication can be transmitted as an indicator message prior to thepoint in time at which data transmissions in this mode begin. Or,alternatively, one or more indicator bits can be transmitted atsubstantially the same time as that in which the bit streams aretransmitted in block 250. For instance, there could be a separatechannel that the mobile monitors just before, or at the beginning of thereception of a bit stream to determine whether to receive the bit streamacross two channels. This would be of value in a telecommunicationssystem in which several remote stations share a dedicated secondaryWalsh code, and wherein a given remote station can begin decoding asecond channel with that dedicated Walsh code shortly after receiving anindicator bit instructing it to do so.

The process then returns to block 242.

Returning to block 246, if it is determined that the communicationsystem will not benefit from transmitting data to a particular remotestation across two channels, the process proceeds to block 252. In block252, a standard rate encoded bit stream is transmitted over a primarychannel. In one embodiment, one in which the encoder produces a singlelower rate encoded bit stream, the standard rate encoded bit stream tobe transmitted is extracted from the lower rate encoded bit stream. Forexample, the odd bits could be extracted to form the standard rateencoded bit stream. In an alternate embodiment, one in which the encoderproduces both a lower rate encoded bit stream and a standard rateencoded bit stream, no extraction of bits is necessary. In such anembodiment, the standard rate encoded bit stream is simply transmittedon a primary channel. The process then returns to block 242.

One skilled in the art will appreciate that in alternate embodiments theblocks need not be in the order they appear in FIG. 2. For instance, oneskilled in the art will appreciate that in one alternate embodiment,block 244 and block 246 could be reversed, such that the decision ofwhether to transmit a lower rate encoded bit stream is made prior to thegeneration of the encoded bit stream. One embodiment in which thedecision of whether to transmit a lower rate encoded bit stream is madeprior to the generation of the encoded bit stream is shown in FIG. 5.

FIG. 5 is an alternative block diagram of a signal transmission method1240 in accordance with one embodiment of the present invention. Insignal transmission method 1240, a base station information bit streamto be transmitted to a remote station is received for encoding in block1242.

The process then moves from block 1242 to block 1246. Block 1246 isrepresentative of a decision block wherein it is determined whether asingle standard rate encoded bit stream should be transmitted on asingle channel or whether a lower rate encoded bit stream should betransmitted in portions over two channels. Any parameter(s) within aCDMA communication system can be used as the basis of the decision indecision block 1246. The only criterion for selecting a parameter foruse in decision block 1246 is whether the parameter can be used tooptimize the communication system in some way. Thus, the qualitydetermination made in decision block 1246 can be made based on any oneof a large number of different quality factors. A straightforward way tomake the decision is to have the transmitter recognize that it istransmitting at a high power level, and that it should switch from onetransmit stream to two transmit streams.

In one embodiment, in block 1246, it is determined whether the amount oftransmit power that would be utilized to transmit the data as a singlestandard rate encoded bit stream is above a predetermined threshold. Thepower level of the transmission is increased as necessary in order tomaintain a desired bit error rate, but the power level can not beincreased without limit. Thus, in decision block 1246 a determination ismade as to whether “excessive” transmission power is required tomaintain the bit error rate. If the transmission power is deemed“excessive,” then the process proceeds to block 12441 wherein a lowerrate encoded bit stream is generated, and subsequently transmitted ontwo channels in block 1250. This occurs because a base station that istransmitting signals to a remote station at an excessively high powerlevel can significantly lower its transmit power level by transmittingthe signal at a lower code rate over two channels. Due to thesignificant decrease in transmit power achieved, system capacity islikely greater in this case, even with the loss of a Walsh code, than ifthe transmit power to this remote station remained excessive and theWalsh code had been saved.

In one embodiment, in decision block 1246, it is also checked whetherthe number of spreading codes presently available is above apre-determined first threshold value. In such a case, not only must“excessive” power be determined, but also the number of availablespreading codes must be above the first threshold value in order for theprocess to move to block 12441. The first threshold value is zero in oneembodiment, meaning that there must be at least one available spreadingcode. This check is done because, although it is desirable to reducepower by transmitting data over two channels, a code needs to beavailable to allocate to the secondary channel.

In one embodiment, in decision block 1246, it is determined whether theremote station is in soft-handoff or in softer-handoff. As is known inthe art, when a remote station is in soft-handoff or softer-handoff, aremote station has communication channels open with more than one cellsite sector. Hereinafter, soft-handoff shall be used to refer to bothsoft-handoff and softer-handoff. If it is determined that a remotestation is in soft-handoff, then the process moves to block 12441wherein the lower rate encoded bit stream is generated, and subsequentlytransmitted in block 1250, as described below. The reason the processmoves to block 12441 is as follows. In a conventional system each sectorwould transmit the same standard encoded bit stream using one channel(Walsh code) per sector. Using the method of the present embodiment usesno extra channels in this instance, because only two channels areneeded, and they would have been used in the conventional system duringsoft-handoff anyway. Proceeding to block 12441, and subsequently toblock 1250, thus does not use any extra channels (Walsh codes), yet ityields the gain described in reference to blocks 12441 and 1250. Namely,less power can be used when transmitting a lower encoded rate bit streamthan when transmitting a standard encoded rate bit stream. Thisrelationship holds true even when the same standard encoded bit streamis transmitted on multiple channels, as it is in a conventional systemwhile a remote station is in soft-handoff. Thus, due to the increasedsystem performance from the power savings that can be obtained, theprocess moves to block 12441, and subsequently to block 1250, when theremote station is in soft-handoff.

In one embodiment a pre-determined second threshold value can be used inblock 1246 to determine whether or not to move to block 12441irrespective of whether or not it is determined that “excessive” poweris being used to transmit to the remote station. In such a case, if thenumber of available spreading codes is above the second threshold value,thus indicating that using an extra code for the call in question wouldlikely not cause a shortage of codes that would reduce system capacity,then the process would proceed to block 12441, irrespective of whetherthe amount of power being used to transmit to the remote station isexcessive. In this case, although the transmitter's power might not beexcessive, reducing the transmitter's power by any amount will stillbenefit the wireless system because it reduces the likelihood ofinterfering with other cells. Because there is presently no shortage ofspreading codes, and the likelihood is low that there will be a shortageof spreading codes anytime soon (as determined by comparing the numberof available codes with a second threshold value), it is beneficial touse one of the spreading codes to reduce transmit power, thus increasingsystem performance.

One skilled in the art will appreciate that decision block 1246 can useany combination of the above embodiments, or it can use any otherembodiments that can determine whether transmitting data to a particularremote station across two channels will optimize the communicationsystem, to decide whether or not to proceed to block 12441 in which thelower rate encoded bit stream is transmitted on two channels. One simpleembodiment that can be used in decision block 1246 is to check thesetting of a flag, variable, or register, to determine whether or notthe communication system will benefit from transmitting data to aparticular remote station across two channels. This is useful in acommunication system wherein a complex determination is first made thattwo channels should be used for transmission, after which after which anindicator message is sent to the remote station to indicate that a lowerrate encoded bit stream will be transmitted on two channels at apredetermined point in time in the future. A flag is then set in thetelecommunication system to indicate that future bit streams should betransmitted across two channels at a predetermined point in time. Insuch a case, just a flag would need to be checked in block 1246.

If, in block 1246, it is determined that the communication system willbenefit from transmitting data to a particular remote station across twochannels, the process proceeds to block 12441. Otherwise, the processproceeds to block 12442.

In block 12441 the information bit stream is encoded into a lower rateencoded bit stream to decrease the required Eb/No needed to transmit thebits to a remote station (as mentioned earlier, a lower code rategenerates more bits than a higher code rate). In an exemplaryembodiment, the encoder is a rate ¼ turbo encoder. However, it should benoted that various encoder rates and types can be used. In an exemplaryembodiment, the encoder has a property such that the odd bits of the ¼rate encoded bit stream make up a ½ rate encoded bit stream, and theeven bits make up a second ½ rate encoded bit stream. In other words,bits 1, 3, 5, etc. make up one ½ rate encoded bit stream and bits 2, 4,6, etc make up a separate ½ rate encoded bit stream. All of the bits,however, comprise the ¼ rate encoded bit stream. In the aforementionedembodiment, the ¼ rate encoded bit stream is the lower rate encoded bitstream referenced earlier. In alternate embodiments the bits arearranged such that a different combination of the bits makes up the two½ rate streams (e.g., the first n/2 bits comprise one ½ rate encoded bitstream, while the second n/2 bits comprise a second ½ rate encoded bitstream). In alternate embodiments the lower rate encoded bit stream isnot comprised of two standard rate encoded bit streams.

The process then moves to block 1250.

In block 1250, a first portion of the lower rate encoded bit stream istransmitted on a primary channel, while a second portion is transmittedon a secondary channel. In one embodiment, the two separate standardrate encoded bit streams that make up the lower rate encoded bit streamare transmitted over a primary and secondary channel. For example, ifthe lower rate encoded bit stream is a ¼ rate bit stream comprising botha standard ½ rate encoded bit stream in its odd bits and a standard ½rate encoded bit stream in its even bits, then the odd bits of thestream would be transmitted over a primary channel and the even bitswould be transmitted over a secondary channel. In the aforementionedembodiment the portions transmitted are of equal length. However, thepresent invention is not limited to such an embodiment. In alternateembodiments, portions of varying length can be transmitted on multiplechannels. For instance, an encoded bit stream could have one third ofits bits transmitted on a primary channel and the remaining two thirdsof its bits transmitted on a secondary channel.

The use of two channels rather than one results in a higher gain withinthe communication system. The second transmission channel can beestablished when needed or it can already be in use. Additionally, morethan one remote station operating according to transmission method 1240can share a secondary channel.

It will be understood that performing signal transmission in this mannerrequires a base station to use two Walsh codes rather than one.Furthermore, it will be understood that when performing signaltransmission is this manner, the transmit power of each of thetransmission channels of block 1250 can be less than one half thetransmit power needed to maintain a desired bit error rate had only asingle channel been used. Thus, the peak power requirement fortransmitting the encoded information signal is reduced by more than onehalf.

When transmitting data in this mode, the communication system needs toindicate to the remote station that it needs to begin receiving bitstreams at a lower code rate, wherein the bit streams are transmitted inportions amongst multiple channels. As stated in relation to block 1246,this indication can be transmitted as an indicator message prior to thepoint in time at which data transmissions in this mode begin. Or,alternatively, one or more indicator bits can be transmitted atsubstantially the same time as that in which the bit streams aretransmitted in block 1250. For instance, there could be a separatechannel that the mobile monitors just before, or at the beginning of thereception of a bit stream to determine whether to receive the bit streamacross two channels. This would be of value in a telecommunicationssystem in which several remote stations share a dedicated secondaryWalsh code, and wherein a given remote station can begin decoding asecond channel with that dedicated Walsh code shortly after receiving anindicator bit instructing it to do so.

The process then returns to block 1242.

Returning to block 1246, if it is determined that the communicationsystem will not benefit from transmitting data to a particular remotestation across two channels, the process proceeds to block 12442. Inblock 12442, a standard rate encoded bit stream is generated. In oneembodiment, only a standard rate encoded bit stream is generated inblock 12442. In an alternate embodiment, a lower rate encoded bit streamis first generated, and then a standard rate encoded bit stream isextracted from bits of the lower rate encoded bit stream. The processthen moves to block 1252, wherein the standard rate encoded bit streamis transmitted over a primary channel. The process then returns to block1242.

FIG. 3 illustrates a code generator system 20. Encoder systems such ascode generator system 20 can be used to generate a code having arequired code rate R by extracting a portion of the output of a lowerrate code. For example, in code generator system 20, two sets of ½ ratecoded bit streams are provided by using a ¼ rate encoder 24. FIG. 3Ashows a flowchart of a method 100 for forming a lower rate R codedbitstream by the code generator system 20. Information bits 22 ofencoder system 20 are applied to ¼ rate encoder 24 to produce R=¼ codedbit stream 26, at block 102. In an exemplary embodiment the odd bits ofthe output make up a ½ rate coded bit stream and the even bits make up asecond ½ rate coded bit stream. Thus, when the portion of odd bits isextracted from R=¼ coded bit stream 26, a first R=½ coded bit stream 28is generated, at block 104. Likewise, when the portion of even bits isextracted from R=¼ coded bit stream 26, a second R=½ coded bit stream 30is generated, at block 106. Thus a code rate R=½ can be generated byextracting a predefined set of bits from the output of R=¼ rate encoder24. A remote station receiving both R=½ coded bit stream 28 on a primarychannel, at block 112 (FIG. 4A), and R=½ coded bit stream 30 on asecondary channel, at block 114, can combine the bits together intotheir correct predefined positions, at block 118, and decode the fullR=¼ coded bit stream 26, at block 120. It is understood by one skilledin the art that in alternate embodiments encoder system 20 couldcomprise an encoder that encodes at a different code rate R and/or thatgenerates a coded bit stream of higher code rates in patterns other thana 2R code rate bit stream located in the odd bits and a 2R code rate bitstream located in the even bits.

Thus code generator system 20 can be used to generate a lower rateencoded bit stream containing a first and second portion of bits, eachof which comprises a first standard rate encoded bit stream and a secondstandard rate encoded bit stream, respectively. The first standard rateencoded bit stream and the second standard rate encoded bit stream canbe transmitted to the remote station where they can be combined anddecoded. Using this method of transmission permits all of theinformation of the unencoded information bit stream to be decoded by theremote station from a single one of the two encoded signals received onone of the two channels used for transmission. This permits the receiverto decode the signal even if one of the transmissions is not received.However, a decoding performed using only one of the encoded signals isless robust than a decoding performed using both encoded signals.Therefore, both encoded signals should be used if they are available.

Code combining methods suitable for use in combining the encoded streamsare well known in the art. It is understood by one skilled in the artthat if a remote station receives only a subset of the encoded streamsprovided in the generalized case it can still decode the informationbits, with reduced decoding performance. It will be understood by oneskilled in the art that encoders of other rates, R, can be used in otherembodiments.

In FIG. 4, there is shown CDMA communication system 30. CDMAcommunication system 30 includes base stations 32, 34 located inadjacent sectors S₁ and S₂ and remote stations 36, 38. In CDMAcommunication system 30 remote stations 36, 38 suffer the worsttransmission interference when they are at the edge of a cell. The majorreason for this is that the propagation loss is largest when they arefarthest from base stations 32, 34. Additionally, remote stations 36, 38are closest to interfering cells at this point. It is thereforedesirable to improve the decoding results when remote stations 36, 38are at the edge of a cell.

Conventionally a communication link is established between remotestations 36, 38 and all nearby sectors. Remote stations 36, 38 receivethe same coded bits from each of the nearby sectors and combine them inpower, in a conventional system. This process is referred to as softhandoff for sectors belonging to different cells and softer handoff forsectors in the same cell. The method of the present embodiments can beadvantageously applied to both soft and softer handoff.

In the method of the present embodiments, in the case of soft handoffeach sector encodes the same information bits. However, the encoding isnot necessarily performed with the same code. In the method of thepresent embodiments, remote station 36 can initiate a call when it islocated well within an initial sector S₁. In this case, sector S₁transmits the information bits encoded with a code C₁ of rate R₁ overcommunication link 33. Remote station 36 can then move to the boundarybetween the original sector S₁ and another sector S₂. In FIG. 4, remotestation 36 is at the boundary between sector S₁ and another sector S₂.At this point, remote station 36 goes into soft handoff with the twosectors. In one embodiment of the invention, sector S₂ transmits thesame information bits encoded with a code C₂ of rate R₂ over acommunication link 35. If the R₁ and R₂ codes are chosen correctly,remote station 36 can combine the stream of coded bits from sector S₁with the coded bits from sector S₂ in such a way that it obtains theequivalent of information bits coded with a code of rate1/((1/R₁)+(1/R₂)). For example, if code rate R₁=½ and code rate R₂=½,the remote station could combine the coded bit streams into a singlecoded bit stream of R=¼ in the method of the present embodiments.

With reference to FIG. 4 and FIG. 4A, remote station 36 has,to correctlycombine the bits. In the example of a lower rate coding scheme whereinthe odd bits make up a first standard rate encoded bit stream and theeven bits make up a second standard rate encoded bit streams, the oddbits will be transmitted from one sector and the even bits will betransmitted from another sector. The remote station needs to know apriori which sector is transmitting the odd bits and which istransmitting the even bits, at block 116, so that it can properlyassemble the lower rate encoded bit stream from the two standard rateencoded bit streams, at block 118. In one embodiment of the invention, ahandoff direction message, presently used to instruct a remote stationto enter soft handoff with a particular sector, will contain one or morebits that indicate to the remote station how to combine the bits fromeach sector per block 116.

In one embodiment, a separate message of one or more bits in the handoffmessage (e.g., extended handoff direction message in cdma2000) informsthe remote station how the bits from a particular channel on aparticular sector should be combined with the bits from other channelson other sectors. For instance, if a system were to use the odd bit/evenbit method of encoding, as described earlier, a base station could senda handoff redirection message to remote station 36 using one bit in thatmessage to tell the remote station whether the bits from Sector S2should be treated as the odd bits or the even bits in the stream, andusing one bit telling the remote station how the bits from Sector S2should be treated.

In another embodiment, the bits are ordered in a pre-determined fashionin accordance with the base station identifiers associated with thechannels of the communication with a remote station. For example, in oneembodiment a system could be designed wherein when a remote station isin soft handoff, the odd bits of a lower rate encoded bit stream will betransmitted from the base station involved in the communication that hasthe lowest base station identifier, while the even bits of the lowerrate encoded bit stream will be transmitted from the other base stationsinvolved in the communication. For instance, if a remote station were ina soft-handoff with base stations having identifiers of B and C (notshown), base station B would transmit the odd bits of a lower rateencoded bit stream while base station C would transmit the even bits.

If the remote station subsequently goes into a three-way handoff, withbase stations A, B, C (not shown), for example, then one of severalembodiments could take place.

In one such embodiment, the portions are not dynamically assigned to thenew/third base station, but instead a new base station always gets afixed portion of bits to transmit. This works in a three-way handoffbecause the first two base stations are already transmitting all thebits in the lower rate encoded bit stream, and the third base station ismerely used for redundancy. For instance, the third base station canalways transmit the even bits. In the above example, wherein basestation A is used for a three-way handoff, base station A transmits theeven bits, while the existing base stations, B and C transmit theportion of bits that they were transmitting in the two-way handoffsituation (odd and even bits, respectively). This is done so that lessdynamic changes are needed to be made to the two channels alreadyinvolved in the call.

In another embodiment, the portions transmitted are dynamicallyreassigned to all base stations upon entering a three-way handoff. Inthis embodiment, the ids are all compared with each other, and the basestation with the lowest ID transmits one portion of bits while the otherbase stations transmit the other portion of bits. Thus, using basestations A, B, and C, again, the odd bits would be transmitted on basestation A, while the even bits would be transmitted on base stations Band C.

When communication from one of the base stations is terminated, suchthat either the remote station exits soft-handoff altogether, orswitches from a three-way handoff to a two-way handoff, the remotestation needs to know how the bits are being transmitted on theremaining base stations.

In one embodiment, when the remote station exits soft-handoff, theexisting base station simply transmits a standard rate encoded bitstream, which the remote station decodes.

In one embodiment, when the remote station goes from a three-way handoffto a two-way handoff, the base stations continue transmitting theportion of the encoded bit stream that they were transmitting before. Inthis embodiment, if they were both transmitting different portions ofthe lower encoded bit stream (e.g., one base station was transmittingodd bits and one was transmitting even bits), the remote stationcombines them into a lower rate encoded bit stream. If, however, theywere both transmitting the same portion of the lower rate encoded bitstream (e.g., both base stations transmitting even bits), then theremote station just decodes each received bit stream as a standard rateencoded bit streams. In such a case, as long as the remote stationremains in a two-way handoff, the bit streams received are handled asthey are in a conventional system.

In another embodiment, the portions transmitted are dynamicallyreassigned to all base stations upon going from a three-way handoff to atwo-way handoff. In this embodiment, the IDs are all compared with eachother, and the base station with the lowest ID transmits one portion ofbits while the other base stations transmit the other portion of bits.Using this embodiment allows the remote station in a two-way handoff tocombine the two bit streams into a lower rate encoded bit streamregardless of whether the two base stations in question weretransmitting the same bit streams while in a three-way handoff.

Remote station 38 can also use the method of the present invention atthe boundary of cell or in a difficult situation such as a fade even ifit has not established communication links with multiple sectors. It isusually not desirable to use additional channels for all remote stationsat all times because the additional channels consume code channels andcells can run out of code channels. This reduces the capacity of thecommunication system due to code limitations. Therefore, in oneembodiment, additional code resources are allocated to remote stationsthat are using larger amounts of power due to poor channel conditions.In this way a cell can dynamically add and remove additional codechannels for each remote station in order to maintain the codeconsumption and the power consumption in balance with each other.

Remote station 38, which is using much power because it is on theboundary of a cell, can use two channels 40, 42 transmitted from thesame sector S₁ when desirable. Each channel 40, 42 can contain the sameinformation bits encoded with a different code, thus decreasing theEb/No required for remote station 38. One of these channels is theprimary channel and one of these channels is the secondary channel.

When a remote station is not in handoff, such as is the case asdiagrammed with remote station 38, a base station can use a fundamentalchannel and a supplemental channel to transmit a lower encoded rate tothe remote station. In one embodiment, a methodology can be used suchthat one portion of bits from the lower encoded bit stream is alwaystransmitted on the primary channel and another portion of bits is alwaystransmitted on the supplemental channel (e.g., odd bits go to theprimary channel, while even bits go to the supplemental channel). Inanother embodiment, the base station can send a message to the remotestation informing it which portion of the lower encoded bit stream willbe transmitted on the primary channel, and which will be transmitted onthe supplemental channel.

It will be understood by one skilled in the art that the invention isnot limited to the above embodiments of methods of transmission, nor theexamples given above. In particular, the example of odd bits and evenbits has been used throughout this application for consistency. However,as described in reference to block 240 of FIG. 2, it is readilyunderstood that other means of portioning the lower rate encoded bitscan be used as well.

By decreasing the amount of power needed by remote stations that areconsuming a high level of power at any given moment, the presentembodiments serve to increase the number of users or the throughput thata telecommunications system can support at any given moment.

FIG. 6 is a block diagram showing a simplified illustration of a remotestation. Digital demodulator 620, Walsh despreading unit 630, blockdeinterleaver 640, convolutional decoder 650, and control processor 660are coupled via a digital bus, and RF receiver 610 is coupled to digitaldemodulator 620. In one embodiment, control processor 660 can activateRF receiver 610 and digital demodulator 620 to receive and processsignals, and can deactivate them when in a power savings mode, such as aslotted-paging mode. Likewise, in one embodiment, control processor 660can selectively activate and deactivate block deinterleaver 640 andconvolutional decoder 650. The RF receiver 610 downconverts anddigitizes RF signals, and provides the digitized signal to digitaldemodulator 620, which performs digital demodulation using PNdespreading techniques, further described in reference to FIG. 7. Thedigitally demodulated data is passed to Walsh despreading unit 630,which performs Walsh despreading techniques, further described inreference to FIG. 7, and produces at least one bit stream output. Forcoded channels, such as traffic channels, the bit stream output isprovided to block deinterleaver 640. In an embodiment that supports anuncoded auxiliary channel, such as a quick paging channel, which is anuncoded channel that uses on-off keying (OOK) modulated direct sequencespread spectrum, the bit stream output for the uncoded auxiliarychannels is provided from Walsh despreading unit 630 to controlprocessor 660 as an uncoded bit stream for further processing. In regardto coded channels, deinterleaver 640 deinterleaves the bit stream outputprovided by Walsh despreading unit 630, and provides a deinterleavedoutput stream to convolutional decoder 650. Convolutional decoder 650uses convolutional decoding techniques known in the art, such as Viterbidecoding or Turbo decoding, to attempt to correct bit errors thatoccurred to the informational bit stream that was transmitted over awireless environment. The convolutionally decoded bit stream is providedto control processor 660 for further processing.

In one embodiment, after receiving an indicator message, controlprocessor 660 instructs digital demodulator 620 and Walsh despreadingunit 630 to switch from a conventional mode of receiving data to a modeof the present embodiments in which data is received at a lower encodedrate across two channels. Likewise, control processor 660 can instructdigital demodulator 620 and Walsh despreading unit 630 to switch from amode of the present embodiments back to a standard data reception modeafter a predetermined time, or upon the receipt of another message froma base station instructing it to exit a mode of the present embodiments.

In one embodiment control processor 660 monitors the uncoded bit streamfor indicator messages. In one embodiment control processor 660 monitorsthe convolutionally decoded bit stream for indicator messages.

One skilled in the art will recognize that control processor 660 may beimplemented using field-programmable gate arrays (FPGA), programmablelogic devices (PLD), digital signal processors (DSP), one or moremicroprocessors, application specific integrated circuit (ASIC) or otherdevices capable of performing the functions described above.

FIG. 7 is a block diagram of a portion of digital demodulator 620 andWalsh despreading unit 630 that can be used to receive data in a datareception mode of the present embodiments in which data is encoded usinga lower rate of encoding and is transmitted in portions over a primaryand secondary channel, wherein the transmissions of the primary andsecondary channel originate from the same base station.

PN despreader 710 is a complex PN despreader which performs PNdespreading, well known to one skilled in the art, on a digitized signalinput (from RF receiver 610) and produces an in-phase (I) and aquadrature-phase (Q) component of the PN despread signal, each of whichis provided to Walsh despreaders 720 and pilot filters 740 as inputsignals.

Walsh despreader 720 a multiplies the I 712 and the Q 714 inputs by afirst Walsh code, which corresponds to the primary channel over which afirst portion of a lower encoded rate bit stream was transmitted, andsums the despread signal over one Walsh symbol, thus producing asoutputs Walsh despread I 722 a and Walsh despread Q 724 a. I 722 a and Q724 a are provided as input to dot product 750 a.

Walsh despreader 720 b multiplies the I 712 and the Q 714 inputs by asecond Walsh code, which corresponds to the secondary channel over whicha second portion of a lower encoded rate bit stream was transmitted, andsums the despread signal over one Walsh symbol, thus producing asoutputs Walsh despread I 722 b and Walsh despread Q I 724 b. I 722 bandQ 724 b are provided as input to dot product 750 b.

In one embodiment, pilot filters 740 are low pass filters that are usedto remove some of the noise from the received signal. In alternateembodiments, pilot filters 740 consist of a Walsh despreader, similar toWalsh despreader 720 a but that despreads with a different Walsh code,immediately followed by a low pass filter. As would be evident to oneskilled in the art, I 742 and Q 744 are essentially smoothed-overestimates of the pilot signal. It would also be evident to one skilledin the art that the pilot signal could consist of a few bitsoccasionally inserted in either or both data streams, and extracted atthe output of Walsh despreaders 720 a and 720 b.

Dot products 750 function as what is known in the art as a conjugatecomplex product with the output of the pilot filter. Dot products 750produce I and Q signal outputs that are estimates of the I and Q valuestransmitted on the data channels. Such dot product apparatus are knownto those skilled in the art. An exemplary embodiment of a dot productapparatus is illustrated in FIG. 8.

The outputs of dot product 750 a, namely I 752 a and Q 754 a, are the Iand Q components of the primary channel, and are provided to symbolextractor 760 a. This will be called the primary symbol extractor,because it extracts the symbols corresponding to the primary channel.The outputs of dot product 750 b, namely I 752 b and Q 754 b, are the Iand Q components of the secondary channel, and are provided to symbolextractor 760 b. This will be called the secondary symbol extractor,because it extracts the symbols corresponding to the secondary channel.

Each symbol extractor 760 yields a series of symbols 762 based upon thetype of modulation used. In an exemplary embodiment in which the datawas transmitted using QPSK modulation techniques, symbol extractor 760yields two symbols 762 for each pair of I and Q inputs 752 and 754. Inanother exemplary embodiment in which the data was transmitted usingBinary Phase Shift Keying (BPSK) modulation techniques, symbol extractor760 yields one symbol 762 for each pair of I and Q inputs 752 and 754.Symbol extractor 760 provides these symbols to summing unit 768. Oneskilled in the art will understand that in alternate embodiments thatuse other modulation techniques, symbol extractor 760 may be absent, inwhich case complex I and Q signals 752 and 754 could be directlysupplied to summing unit 768, or directly supplied to MUX 770 (in anembodiment in which summing unit 768 is also absent).

Two-channel finger 780 a is representative of a two-channel finger thatis used to track two channels (a primary and a secondary) from a singletransmission signal generated by a single base station. Each two-channelfinger 780 produces a primary and a secondary channel output. In anembodiment in which symbol extractors are present, the primary channeloutput of a two-channel finger 780 is the output of the primary symbolextractor (e.g., 762 a in FIG. 7), while the secondary channel output isthe output of the secondary symbol extractor (e.g., 762 b in FIG. 7). Inan alternate embodiment in which symbol extractors are not present, theprimary channel output is the primary I and Q values (e.g., 752 a and754 a), while the secondary channel output is the secondary I and Qvalues (e.g., 752 b and 754 b).

To account for multi-path signals that can occur, the outputs from aplurality of two-channel fingers 780, each of which tracks the receivedsignals at a slightly different

PN offset or time delay, are supplied to summing unit 768. Summing unit768 sums the primary channel output produced by each two-channel finger780, and provides it to MUX 770. Additionally, summing unit 768 sums thesecondary channel output produced by each two-channel finger 780, andprovides the summed value to MUX 770. As is known to one skilled in theart, a summer is used to combine the output of multiple fingers in orderto generate a better estimate of the transmitted I and Q or symbolvalues. In some embodiments, summing unit 768 may also rescale thesignals in order to keep the signal within an acceptable dynamic range.The combined estimate need not be generated prior to MUX 770, but canrather be generated after MUX 770 in alternate embodiments. In analternate embodiment, summing unit 768 is not present prior to MUX 770,in which case the primary channel outputs and secondary channel outputsfrom each two-channel finger 780 are supplied directly to MUX 770.

In one embodiment, MUX 770 is a multiplexer that receives as inputprimary channel data and secondary channel data from summing unit 768,which MUX 770 arranges into a single symbol stream that is provided toblock deinterleaver 640. The symbols are arranged in accordance with themethod used to transmit the data over the two channels. For instance, inan exemplary embodiment in which the odd bits are transmitted on theprimary channel and the even bits are transmitted on the secondarychannel, MUX 770 arranges the symbols 762 such that the estimate of thefirst received symbol corresponding to the primary channel will befollowed by the estimate of the first received symbol corresponding tothe secondary channel. In such an embodiment, this process repeats,wherein another symbol is output corresponding to the primary channel,followed by another symbol corresponding to the secondary channel. Thesymbol stream yielded by MUX 770 is supplied to convolutional decoder650, further described in reference to FIG. 6.

An exemplary embodiment of dot product 750 is diagrammed in FIG. 8. InFIG. 8, I 742 and I 722 are complex multiplied in complex multiplier 810a, while I 742 and Q 724 are complex multiplied in complex multiplier810 b. Likewise, Q 744 and Q 724 are complex multiplied in complexmultiplier 810 c, while Q 744 and I 722 are complex multiplied incomplex multiplier 810 d. The output of complex multiplier 810 a is thensummed with the output of complex multiplier 810 c in combiner 820 a,thus producing I 752. The output of complex multiplier 810 d issubtracted from the output of complex multiplier 810 b in combiner 820b, thus producing Q 754.

FIG. 9 is a block diagram of a portion of digital demodulator 620 andWalsh despreading unit 630 that can be used to receive data in a datareception mode of the present embodiments in which data is encoded usinga lower rate of encoding and is transmitted in portions over a primaryand secondary channel, wherein the transmissions of the primary andsecondary channel originate from different base stations, or wherein thetransmissions of the primary and secondary channel originate from thesame base station (the latter provides an alternative to the apparatusdescribed in reference to FIG. 7 in the case where the primary andsecondary channel originate from the same base station).

PN despreader 910 a is a complex PN despreader which performs PNdespreading, well known to one skilled in the art, on a digitized signalinput (from RF receiver 610)and produces an in-phase (I) and aquadrature-phase (Q) component of the PN despread signal, each of whichare provided to Walsh despreaders 920 and pilot filters 940 as inputsignals. PN despreader 910 a is used to decode a primary channel from afirst base station.

PN despreader 910 b is a complex despreader that functions like PNdespreader 910 b. PN despreader 910 b behaves differently in that it isused to decode a secondary channel from a second base station. In oneembodiment PN despreader 910 b uses the same PN code for despreading asPN despreader 910 a, but at any given time PN despreader 910 b decodeswith a different portion of the PN code than does 910 a. In such anembodiment, the portion of the PN code used by each decoder for decodingat any given moment is determined by the PN offset associated with thebase station it is decoding a channel from. As the PN offset for thefirst base station is different from the PN offset of the second basestation in such an embodiment, the two PN despreaders 910 decode thereceived signal using different portions of the PN code at any givenmoment. In an alternate embodiment, PN despreader 910 a uses a differentPN code for despreading the received signal than does PN despreader 910b. In another alternate embodiment, for use in the case in which theprimary and secondary channel transmissions originate from the same basestation, one primary channel PN despreader 910 a and one secondarychannel PN despreader 910 b use the same PN code and the same PN offsetto decode the transmission; this can be used in lieu of a singletwo-channel finger 780 a, described in reference to FIG. 7.

Walsh despreader 920 a multiplies the I 912 a and the Q 914 a inputs bya first Walsh code, which corresponds to the primary channel over whicha first portion of a lower encoded rate bit stream was transmitted, andsums the despread signal over one Walsh symbol, thus producing asoutputs Walsh despread I 922 a and Walsh despread Q 924 a. I 922 a and Q924 a are provided as input to dot product 950 a.

Walsh despreader 920 b multiplies the I 912 b and the Q 914 b inputs bya second Walsh code, which corresponds to the secondary channel overwhich a second portion of a lower encoded rate bit stream wastransmitted, and sums the despread signal over one Walsh symbol, thusproducing as outputs Walsh despread I 922 b and Walsh despread Q 924 b.I 922 b and Q 924 b are provided as input to dot product 950 b.

In one embodiment, pilot filters 940 are low pass filters that are usedto remove some of the noise from the received signal. In alternateembodiments, pilot filters 940 consist of a Walsh despreader, similar toWalsh despreader 920 a but despreading a different Walsh code,immediately followed by a low pass filter. As would be evident to oneskilled in the art, I 942 a and Q 944 a are essentially smoothed-overestimates of the pilot signal of the first base station. It would alsobe evident to one skilled in the art that the pilot signal of the firstbase station could consist of a few bits occasionally inserted in eitheror both data streams, and extracted at the output of Walsh despreaders920 a. Likewise, as would be evident to one skilled in the art, I 942 band Q 944 b are essentially smoothed-over estimates of the pilot signalof the second base station. It would also be evident to one skilled inthe art that the pilot signal of the second base station could consistof a few bits occasionally inserted in either or both data streams, andextracted at the output of Walsh despreaders 920 b.

Dot products 950 function as what is known in the art as a conjugatecomplex product with the output of the pilot filter. Dot products 950produce I and Q signal outputs that are 750 estimates of the I and Qvalues transmitted on the data channels. Such dot product apparatus areknown to those skilled in the art. An exemplary embodiment of a dotproduct apparatus is illustrated in FIG. 8.

The outputs of dot product 950 a, namely I 952 a and Q 954 a, are the Iand Q components of the primary channel, and are provided to symbolextractor 960 a. This will be called the primary symbol extractor,because it extracts the symbols corresponding to the primary channel.The outputs of dot product 950 b, namely I 952 b and Q 954 b, are the Iand Q components of the secondary channel, and are provided to symbolextractor 960 b. This will be called the secondary symbol extractor,because it extracts the symbols corresponding to the secondary channel.

Each symbol extractor 960 yields a series of symbols 962 based upon thetype of modulation used. In an exemplary embodiment in which the datawas transmitted using QPSK modulation techniques, symbol extractor 960yields two symbols 962 for each pair of I and Q inputs 952 and 954. Inanother exemplary embodiment in which the data was transmitted usingBinary Phase Shift Keying (BPSK) modulation techniques, symbol extractor960 yields one symbol 962 for each pair of I and Q inputs 952 and 954.Symbol extractor 960 provides these symbols to summing unit 968. Oneskilled in the art will understand that in alternate embodiments thatuse other modulation techniques, symbol extractor 960 may be absent, inwhich case complex I and Q signals 952 would be directly supplied tosumming unit 968, or directly supplied to MUX 970 (in an embodiment inwhich summing unit 968 is also absent).

Finger 980 a is representative of a finger that is used to track asingle channel (a primary one) from a single transmission signalgenerated by a single base station. Each finger 980 tracks either aprimary channel or a secondary channel and produces a primary or asecondary channel output accordingly. For instance, finger 980 a tracksa primary channel and therefore produces a primary channel output, whilefinger 980 b tracks a secondary channel and therefore produces asecondary channel output. In an embodiment in which symbol extractorsare present, the primary channel output of a finger 980 that tracks aprimary channel is the output of the primary symbol extractor (e.g., 962a in FIG. 9), while the secondary channel output of a finger 980 thattracks a secondary channel is the output of the secondary symbolextractor (e.g., 962 b in FIG. 9). In an alternate embodiment in whichsymbol extractors are not present, the primary channel output is theprimary I and Q values (e.g., 952 a and 954 a), while the secondarychannel output is the secondary I and Q values (e.g., 952 b and 954 b).

To account for multi-path signals that can occur, the outputs from aplurality of fingers 980, each which track a primary or secondaryreceived signals at a slightly different PN offset or time delay, aresupplied to summing unit 968. Summing unit 968 sums the primary channeloutput produced by each primary channel finger 980, and provides it toMUX 970. Additionally, summing unit 968 sums the secondary channeloutput produced by each secondary channel finger 980, and provides thesummed value to MUX 770. As is known to one skilled in the art, a summeris used to sum the output of multiple fingers in order to generate abetter estimate of the transmitted I and Q symbol values. In someembodiments, summing unit 968 may also rescale the signals in order tokeep the signal within an acceptable dynamic range. The combinedestimate need not be generated prior to MUX 970, but can rather begenerated after MUX 970 in alternate embodiments. In an alternateembodiment, summing unit 968 is not present prior to MUX 970, in whichcase the primary channel outputs and secondary channel outputs from eachprimary channel finger 980 and secondary finger 980, respectively, aresupplied directly to MUX 970.

In one embodiment, MUX 970 is a multiplexer that receives as inputprimary channel data and secondary channel data from summing unit 968,which MUX 970 arranges into a single symbol stream that is provided toblock deinterleaver 640. The symbols are arranged in accordance with themethod used to transmit the data over the two channels. For instance, inan exemplary embodiment in which the odd bits are transmitted on theprimary channel and the even bits are transmitted on the secondarychannel, MUX 970 arranges the symbols 962 such that the estimate of thefirst received symbol corresponding to the primary channel will befollowed by the estimate of the first received symbol corresponding tothe secondary channel. In such an embodiment, this process repeats,wherein another symbol is output corresponding to the primary channel,followed by another symbol corresponding to the secondary channel. Thesymbol stream yielded by MUX 970 is supplied to convolutional decoder650, further described in reference to FIG. 6.

The group of modules located in each box 980 is representative of afinger used to track a signal from a signal base station, without takinginto account multi-path signals that might be received from each basestation as well. Although, for the sake of simplicity, multiple fingersused to track multipath signals is are shown in FIG. 9, one skilled inthe art will understand that to account for a multi-path environmentmore fingers 980 with different PN offsets can be added to trackmultiple multi-path signals from one or more base stations in amulti-path environment.

The previous description of the embodiments is provided to enable aperson skilled in the art to make or use the present invention. Thevarious modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments without the use of the inventivefaculty. Additionally, the various methods taught herein can be combinedwith each other in any manner without the use of the inventive faculty.Thus, the present invention is not intended to be limited to theembodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed.

1. A device for receiving a first and second encoded standard coded rate(SCR) bitstreams over a first and second transmission channels,respectively, in a communication system, the device comprising: a RFreceiver configured to receive the first and second encoded SCRbitstreams transmitted over the first and second transmission channels,respectively, wherein the first and second encoded SCR bitstreams are afirst portion and a second portion of a lower coded rate (LCR)bitstream, and wherein the first encoded SCR bitstream is received froma first sector and the second encoded SCR bitstream is received from asecond sector, and wherein the device is a remote station and the firstand second transmission channels are between the remote station and twoseparate base stations, each base station having a base stationidentifier; and a multiplexer configured to assemble the lower codedrate (LCR) bitstream from the first and second encoded SCR bitstreams,wherein the first SCR bitstream comprises odd bits and the second SCRbitstream comprises even bits and the remote station is configured touse a lowest valued base station identifier to determine the order tocombine the odd and even bits from the two base stations.
 2. The deviceof claim 1 further comprising a convolutional decoder configured todecode the LCR bitstream to obtain an information signal, wherein theinformation signal comprises the first and second encoded SCR bitstreamstogether.
 3. The device of claim 1, wherein the first SCR bitstreamcomprises a first number of bits and the second SCR bitstream comprisesa second number of bits different from the first number of bits.
 4. Thedevice of claim 3, where the RF receiver is further configured toreceive instructions to enter a soft handoff with a particular sector.5. The device of claim 1, wherein the first and second transmissionchannels are from the two separate base stations, respectively, to theremote station.
 6. A method of receiving a first and second encodedstandard coded rate (SCR) bitstreams over a first and secondtransmission channels, respectively, in a communication system from atleast two base stations, the method comprising: receiving the first andsecond encoded SCR bitstreams transmitted over the first and secondtransmission channels, respectively, wherein the first and secondencoded SCR bitstreams are a first portion and a second portion of alower coded rate (LCR) bitstream, wherein the first encoded SCRbitstream is received from a first sector and the second encoded SCRbitstream is received from a second sector, and wherein receiving thefirst and second encoded SCR bitstreams transmitted over the first andsecond transmission channels comprises receiving the first and secondencoded SCR bitstreams respectively from two separate base stations,wherein each base station includes a distinct base station identifier;assembling the lower coded rate (LCR) bitstream from the first andsecond encoded SCR bitstreams based on a predetermined order, whereinthe first SCR bitstream comprises odd bits and the second SCR bitstreamcomprises even bits; and determining the order to combine the odd andeven bits from the two base stations, using a lowest valued base stationidentifier.
 7. The method of claim 6, further comprising: decoding theLCR bitstream to obtain an information signal, the first and secondencoded SCR bitstreams together representing the information signal. 8.The method of claim 6, wherein the first SCR bitstream comprises a firstnumber of bits and the second SCR bitstream comprises a second number ofbits different from the first number of bits.
 9. The method of claim 8,further comprising receiving instructions to enter a soft handoff with aparticular sector.
 10. The method of claim 6, wherein receiving thefirst and second encoded SCR bitstreams transmitted over the first andsecond transmission channels comprises receiving the first and secondencoded SCR bitstreams from the two separate base stations,respectively.